1. Field of the Invention
The invention relates to lighting fixtures, and particularly to fixtures for use in still photography and cinematography.
2. Description of the Related Technology
Photography is the science, art, and practice of creating durable images by recording light or other electromagnetic radiation, either electronically, by means of an image sensor, or chemically, by means of a light-sensitive material such as photographic film. Still photography is the practice of making non-moving photographs, as distinct from motion picture photography (cinematography). Cinematography is the science or art of motion picture photography by recording light or other electromagnetic radiation, either electronically by means of an image sensor, or chemically, by means of a light-sensitive material such as film stock. Photographic lighting is the illumination of scenes to be photographed. A photograph may simply record patterns of light, color, and shade; lighting is important in controlling the image. In many cases even illumination is desired to give an accurate rendition of the scene. In other cases the direction, brightness, and color of light are manipulated for effect. Lighting is particularly important for establishing an interplay of highlights and shadows. Lighting and exposure are used to create effects such as low-key and high-key.
The main sources of light for photography are:                1. Natural/daylight, which varies with the weather and the time of day. Different techniques are necessary to take best advantage of or control the impact of natural light conditions, such as brilliant sunshine, an overcast evening, or any other condition;        2. Continuous artificial light, which may be normal lighting, or produced by special photoflood lights or other fixtures; and        3. A bright and very brief photographic flash from one or more positions.        
The properties of different light sources vary; household incandescent lighting, fluorescent lighting, sodium discharge street lighting, etc., are very different and produce different results, and require different correction if a subjectively neutral or other desired rendition of colors is required.
Lighting creates the two dimensional pattern of contrast the brain interprets to recognize three dimensional objects in photographs. In an in-person viewing experience the brain relies on stereoscopic vision, parallax, shifting focal in addition to the clues created by the highlight and shadow patterns the light on the object creates. When viewing a photographic image the brain tries to match the patterns of contrast and color it seen to those other sensory memories.
The baseline for what seems “normal” in lighting is the direction and character of natural and artificial sources and the context provided by other clues. In the example the photographer added a warming gel on the flash of the woman standing in a field in late afternoon light. The viewer knows the time of day from the angle of the shadows and neutral color balance would have seemed odd in that context. But similarly the image of the woman if masked out and put on a plain white or neutral gray background would seem abnormally yellow.
The goal in all photographs is not necessarily to create an impression of normality. A lighting strategy can be used to achieve an impression that is different than normally expected. Light direction relative to the camera can alter the appearance of a three dimensional object to give a two-dimensional impression. The presence, position, size/length, and direction of highlights and shadows provide other clues to shape and, when outdoors, the time of day. The tone and length of shadows provide contextual clues about the time of day or environment and by inference, based on personal experience, the mood of person.
A skilled photographer can manipulate how a viewer is likely to react to the content of a still or moving photograph by manipulating the lighting. In outdoor photography that can require a change in location, waiting for the ideal time (angle of sunlight) of day or in some cases the ideal time of year for the lighting to create the desired impression in the photograph or manipulating the natural lighting by using reflectors or flash. One of the limits to options for lighting objects to make a photographic image look “seen by eye” normal or surreal as a goal for the photograph is the available equipment. The viewer's reaction to an image(s) will be from the baseline of whether the lighting seems normal/natural or not compared to other clues. For example, when mixing natural artificial lighting, it is possible to control the differences between the shadow clues from the artificial light in coordination to the natural light. A photograph of a person's face artificially illuminated to appear as if it were photographed at noon will not seem normal if the background is illuminated by a setting sun because the lighting clues of the foreground do not match.
The sun hitting the front of objects facing a camera acts as “key” light creating highlights and casting shadows. The detail in the shadows is visible because the sunlight reflects off water vapor and dust in the atmosphere creating omni-directional “fill”. In open shade three dimensional objects will also usually cast shadows because the downward vector of skylight is usually stronger than the sideways vectors illuminating the sides. When a photographer puts a light source behind an object its role in the lighting strategy is to define an outline and create an impression of physical separation and three dimensional space that a frontally illuminated scene lacks. To differentiate that role from that of “key” modeling when a modeling source moves behind the object it is typically called a “rim” or “accent” light. In portrait lighting it also called a “hair” light because it is used to create the appearance of physical separation between the subject's head and background. In natural lighting the tone of the background of an image is influenced by its reflective qualities and whether it is illuminated by the sun directly or skylight indirectly. Either the sun or sky, or a combination of both can be used for “background” lighting.
Artificial lighting strategies which seem most “natural” duplicate the same contrast pattern clues seen on three dimensional objects in various lighting conditions. A typical studio lighting configuration will consist of a fill source to control shadow tone, a single frontal key light to create the highlight modeling clues on the front of an object facing the camera over the shadows the fill illuminates, one or more rim/accent lights to create separation between foreground and background, and one or more background lights to control the tone of the background and separation between it and the foreground. This equipment may be cumbersome to store or transport.
There are two significant differences between natural lighting and artificial sources. One is the character of the fill and the other is more rapid fall-off in intensity. In nature skylight fill is omni-directional and usually brighter from above. That “wrap around” characteristic is difficult to duplicate with a directional artificial source. In a fixed studio location it is possible to bounce fill backwards off a white wall to flood the space with indirect reflected light to simulate the impression of the sun reflecting off the atmosphere. Another way is to supplement a fill source from the direction of the camera with reflectors placed near the sides of the foreground subject.
The inverse-square law describes the approximate way a light source radiates and changes in intensity with distance. As the distance from a source doubles the area of the footprint of light increase by a factor four (the square of the distance). Because the same number of photons are spread over four times the area when distance is doubled the intensity at any point will be or ¼ the strength. Photographic light sources are not point light sources so the inverse square law does not perfectly apply but it explains why distance of artificial sources affects the character of lighting and lighting strategies in ways not seen in nature.
According to the inverse-square law if the distance of a light source is changed in the following distance increments 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64 the intensity will decrease by one f/stop. In practical terms this means if one face in a group portrait is 4 m from the “key” light and another is 5.6 m away the face further from the light will be one f/stop darker. In an outdoor portrait of a group of 200 people taken on an overcast day the lighting on all of the faces will be equal. The same group photographed indoors would be far more difficult to light evenly. The simplest strategy requiring the least lighting equipment would be to get above the group with the camera, have them look up and bounce the lighting off the ceiling so like an overcast day every face is as equidistant as possible to the apparent source of the light.
Even something as basic as a head and shoulders portrait must take inverse-square fall-off into account by posing the front of the subject's face as close or closer to the “key” light than the shoulder or any other body part if the goal is to make the front of the face the most strongly contrasting focal point on a darker background. The position of the fill source relative to the face will also affect whether the nose shadow is the lightest (when fill is centered near camera) darkest (when fill is placed to the side) one on the face. The distance of the key and fill sources to the face will affect the rate at which the shadows transition from light to dark on the face.
A scene may be lit to look natural or surreal. Natural and surreal just describe grossly the effect of lighting. Understanding what makes lighting seem natural makes it easier to understand how to create other desired reactions. Natural light usually comes from above, so strategies which place the key light below the face will appear to be unusual or unnatural. The brain adapts color perception in a way which makes color balance seem neutral on white clothing and faces. The eyes also adapt to brightness as they scan and usually perceive a full range of detail in most environments. Lighting a scene with a tonal range or color cast which is out of context with what would typically be expected will cause the viewer to notice the environment and make other than normal assumptions about it. It is also possible to create the impression of environmental context where none is seen in the photograph, such the look of a person standing under a streetlight at night by using a gridded flash attached to the ceiling of the studio with no fill source.
A reflector is an improvised or specialized reflective surface used to redirect light towards a given subject or scene. Reflectors are often fixed to an artificial light source (for example, a filament bulb or flash tube) to direct and shape the otherwise scattered light by reflecting the light off a concave inner surface and direct the light toward the scene to be photographed. Although there are a large number of variants, the most common types of reflectors are spherical, short-sided, giving a relatively broad spread of light, and parabolic, providing a tighter, parallel beam of light.
The reflector factor is the ratio of the illumination provided by a lamp fitted within a reflector to the illumination provided without any reflector fitted. A matte reflector will typically have a reflector factor of around 2, due to its more diffuse effect, while a polished or metallic-finished reflector may have a factor of up to 6.
A Soft box is a type of photographic lighting device, one of a number of photographic soft light devices. Soft light fixtures create even and diffused light by directing light through some diffusing material, or by “bouncing” light off a second surface to diffuse the light. Light from a bulb may be bounced off the inside of a metalized umbrella to create a soft indirect light in a known umbrella light.
A “soft box” is an enclosure around a bulb comprising reflective side and back walls and a diffusing material at the front of the light.
The sides and back of the box are lined with a bright surface—an aluminized fabric surface or an aluminum foil, to act as an efficient reflector. In some commercially available models the diffuser is removable to allow the light to be used alone as a floodlight or with an umbrella reflector.
A soft box can be used with either flash or continuous light sources such as fluorescent lamps or “hot lights” such as quartz halogen bulbs or tungsten bulbs. If soft box lights are used with “hot” light sources, the user must be sure the soft box is heat rated for the wattage of the light to which it is attached in order to avoid fire hazard.
U.S. Pat. No. 3,851,164 entitled, “Umbrella Light,” is expressly incorporated by reference herein and shows a prior art umbrella light fixture. As shown in FIG. 9, a light source 11 is adjustably fixed to the axial shaft 12 of a foldable umbrella-type reflector 13. The assemblage of umbrella-type reflector 13 and light source unit 11 is adjustably supported on a swivel 14 atop a conventional folding tripod stand having an adjustable telescoping vertical pole 17. The light source unit 11 has a pair of quartz halogen lamps.
The light source unit 11, has the lamps and reflectors in predetermined fixed relationship, is adapted to be secured at any suitable position along the length of the umbrella shaft 12. To this end it has spring clamp 32 for frictionally engaging the shaft 12. The bulbs and their reflectors are not arranged completely symmetrically with respect to the shaft 12 and the umbrella-type reflector carried thereby.
The spring clamp may be a simple conventional spring clip such as is used for holding sheets of paper together, having a pair of spring-loaded jaws generally several cm (e.g., about 5 cm) long and having a pair of finger pieces (e.g., Boston Bull Clip No. 2). One of the finger pieces is secured to the housing of the light source unit 11; the other, projects outwards for manual manipulation and is provided with a heat- and electrically-insulating covering.
The prior art device is configured with light source unit 11 fixed to the swivel 14 such that the center of gravity of the device is situated approximately directly over the pole 17 or base of the tripod. Like conventional umbrellas, the umbrella has, on its central shaft 12, a small ring 56 fixed near the top of the shaft; a set of long ribs 57 each having one end 58 pivotally attached to the small fixed ring 56; a slider 59 mounted on the shaft and having a small ring 61 integral therewith; a set of short ribs 62 each having one of its ends 63 pivotally attached to the slider ring and its other end 64 pivotally attached to the long rib at an intermediate point 66 on the length of said long rib 57 (a pivot fitting 67 being fixed to each long rib for this purpose); a latch 68 to hold the slider 59 in a position on the shaft in which the umbrella is open; a second latch 68a to hold the slider in a position on the shaft in which the umbrella is closed; and a fabric cover 69 which is fixed to the shaft just outside of the fixed ring 58 (being held on the shaft by a suitable ferrule 71) and is attached (as by suitable thread loops 72) to fittings 73 secured to the long ribs 57 adjacent their free ends 74, as well as by intermediate thread loops 76 engaging intermediate portions of said long ribs. As in conventional umbrellas, the covering is made up of series of substantially identical sectors or panels sewn together along their edges, forming seams, and the rib-attaching loops 72 are situated at the outer ends of the seams so that each of the panels is disposed between the corresponding adjacent long ribs. The position of the latch 68 is such that when the slider is held thereby the fabric is taut and the long ribs are bent. The ribs are flexible and of conventional construction, of thin metal which is formed into channel-shaped cross-section over substantially their whole length, except at their ends.
The umbrella is shaped so that in its open operative position it has a central portion, adjacent to its apex, whose fabric surface faces in a direction such as to reflect the light principally in an axial direction and a peripheral portion whose fabric surfaces face in a direction such as to reflect the light principally in a direction which is radial of the axis.
A significant disadvantage to the prior art configurations of umbrella lights as described above, that the weight of the light source unit and the required proximity of the light source unit 11 to the umbrella reflector limits the range of positions for the fixture which must always have a center of gravity above the base of the tripod. The relative position of the pole 17 and the fabric cover limit the orientation of the umbrella type reflector. In addition, the lighting unit, long ribs, short ribs, shaft and mounting pole all interfere with the light projection. The components, particularly the light source unit 11, contributes significant weight and the fixture is bulky, cumbersome to assemble, and requires significant storage space to store.